Manufacturing processes commonly used in conjunction with the production of epoxies include filament winding, pultrusion, infusion molding, resin transfer molding (RTM), vacuum assisted RTM (VARTM), and wet lay-up or vacuum bag techniques. Polyoxyalkylene amines, or “polyetheramines” as they are sometimes called, are useful as curing agents in epoxy systems to improve flexibility, and to lengthen working time in the manufacture of fiber-reinforced composites. The “working time” is defined as the time period between when the reactive components of the epoxy resin are first mixed with one another and when the mixture is no longer suitable for processing. During the working time, the resin or article containing the resin remains in a pourable, flexible, pliable or otherwise mouldable form.
The use of epoxy binders is preferred by many manufacturers of fiber-reinforced composite wind turbine generator (“WTG”) propellers, which propellers each typically comprise three individual epoxy-composite blades having lengths from 20-40 meters each. Unfortunately, the working times provided for by currently-available amine curing agents are insufficient for the preparation of blades having optimal properties. In addition to a longer working time, the materials from which a WTG blade material is made must also maintain good heat resistance when cured.
Many WTG blade manufacturers today use the VARTM process when working with liquid epoxy systems or epoxy polyester systems. These resin systems must cure slowly in a controlled fashion and allow sufficient working time to wet-out the fiberglass, aramid fiber, carbon fiber, or other fibers that are used as reinforcing materials in the wind turbine blades. In some cases, prepreg epoxy systems may be used. In these instances, fibers pre-impregnated with a reasonably latent epoxy resin system may be used to form the turbine blade. The use of polyetheramines as epoxy curing agents is not common in the prepreg materials, but is common practice by some using VARTM and other liquid molding processes, where JEFFAMINE® D-230 amine (Huntsman Corporation, Houston, Tex.) is used in large quantities. However, manufacturers understand that the working time for using such materials is too short for optimum production, mainly when manufacturing individual blades of greater than 30 meters in length. Since the tendency in the WTG industry is to go to longer blade length to increase the ability of each WTG to produce more power/unit, a need has arisen in the art for curing agents which can make the manufacture of such blades commercially viable.